Supermassive though it may be, the heart of the Milky Way’s black hole is not as big as you might think; the event horizon of Sagittarius A* is just 24 million km across – 17 times bigger than the Sun.

At 25,000 light years away, that makes it a pinprick. From the surface of the Earth, Prof [Feryal] Ozel explained, it takes up about as much of the sky as a CD sitting on the moon.

And surrounding this mysterious, spherical frontier are roiling clouds of gas and dust, which blaze with energy as they are sucked and squeezed furiously towards it…

“Hopefully it will look like a crescent – it won’t look like a ring,” Prof Ozel said.

This is because the glowing gas is spinning around the black hole, and a dramatic Doppler effect should make the stuff moving towards the Earth appear much brighter. “The rest of the ring will also emit, but what you will brightly pick up is a crescent.”

Another reason that this black hole image will be a big deal: What we observe may predictably support or fail to comply with Einstein’s theory of general relativity.

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